Document Type


Publication Date




For well over a century, rhizobia have been recognized as effective biofertilizer options for legume crops. This has led to the widespread use of rhizobial inoculants in agricultural systems, but a recurring issue has emerged: applied rhizobia struggle to provide growth benefits to legume crops. This has largely been attributed to the presence of soil rhizobia and has been termed the ‘rhizobial competition problem.’


Microbiome engineering has emerged as a methodology to circumvent the rhizobial competition problem by creating legume microbiomes that do not require exogenous rhizobia. However, we highlight an alternative implementation of microbiome engineering that focuses on untangling the complexities of the symbiosis that contribute to the rhizobial competition problem. We outline three approaches that use different starting inocula to test hypotheses to overcome the rhizobial competition problem.


The approaches we suggest are targeted at various stages of the legume-rhizobium symbiosis and will help us uncover underlying molecular mechanisms that contribute to the rhizobial competition problem. We conclude with an integrative perspective of these different approaches and suggest a path forward for future research on legumes and their complex microbiome.


This article was originally published in Plant and Soil in 2021.


The authors

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.